1. Field of the Invention
The present invention relates to a method for detecting a marked surgical implement such as a sponge, clamp, or catheter within a surgical wound in human or animal tissue irrespective of its position or orientation therewithin.
2. Description of the Prior Art
During the course of a surgical operation it is frequently necessary for articles, such as surgical sponges, gauzes, instruments, needles, and the like, to be placed into a wound cavity. Notwithstanding rigorous precautions attendant surgical procedures, such items are sometimes inadvertently lost during surgery and remain within the patient. When this happens, the patient can encounter serious consequences, including pain, infection, intestinal obstruction, and even death. The problem of retained surgical implements has existed since the earliest days of surgery. Procedures conventionally employed to prevent post-surgical implement retention include a manual search of the wound by the surgeon prior to closure and a careful accounting for all materials inserted and removed from the wound. The accounting function is customarily carried out by the operating room staff, usually the circulating nurse. Despite these precautionary measures the accidental retention of surgical implements continues to occur with disturbing regularity, even in prestigious institutions, and is regarded by surgeons as a major unsolved problem.
At present, manual search and physical count remain the primary methods used in detection of retained surgical implements. Most surgical instruments are composed of metal, and are easily detectable by x-ray. Sponges have been tagged with radiopaque markers to make them also visible on x-ray, but x-rays are not routinely done before completion of the operation because of several disadvantages including inconvenience, expense, loss of operative time, and radiation exposure. Postoperative x-rays suffer from some of the same disadvantages. Moreover, even when postoperative x-rays are taken, retained items are occasionally overlooked; but even if detected, require a second operation to effect their removal.
To overcome the difficulty of detecting retained surgical implements, it has been suggested that the implements be provided with a radioactive tracer. This technique, disclosed by U.S. Pat. No. 2,740,405 to Riordan, is subject to obvious hazards associated with use, storage and disposal of radioactive materials.
It has also been proposed that surgical sponges be marked with a flexible plastic impregnated with either paramagnetic or ferromagnetic materials in the form of powders. Detection of these marked sponges is accomplished by a metal detector. This method, taught by U.S. Pat. No. 3,422,816 to Robinson et al., provides very small signals difficult to detect over the width of a patient's body. In addition, the Robinson et al. technique provides no discrimination against other metal objects, such as staples which, though present within the surgical wound, are appointed for retention therewithin.
Yet another proposal, advanced by U.S. Pat. No. 3,587,583 to Greenberg, involves use of surgical sponges marked with magnetized particles whose presence is detectable with manetodiodes. In practice, however, the magnetic field generated by these particles is too small to be readily detected by the diodes.
U.S. Pat. No. 4,114,601 to Ables discloses the use of a small transponder fixed to a surgical sponge or instrument. This transponder exhibits gyromagnetic resonance at preselected frequencies. Detection is accomplished by nonlinear mixing of two frequencies impinging upon the transponder. The gyromagnetic resonance effect disclosed by Ables is a high frequency phenomenon, existing at frequencies of the order of about 5 gigahertz (5,000,000,000 cycles/sec). These frequencies, known as microwaves, are absorbed readily by animal tissue and are, in fact, used in microwave ovens for cooking. In use of the Ables type transponder, the energy developed goes primarily into heating tissue, rather than exciting the transponder into gyromagnetic resonance.
Other detection systems which have been proposed for use in making and detecting articles are, as presently practiced, not suitable for detection of retained surgical implements. One such detection system, disclosed by U.S. Pat. No. 4,510,489 to Anderson et al., finds utility in antitheft applications, as well as in such applications as access control, vehicle control, document control or product verification. The Anderson et al. apparatus operates by defining an interrogation zone of fixed dimensions. Articles having a marker affixed thereto pass through this zone. The passage of these articles through the zone is critical to certain detection of the marker since, in particular orientations, a stationary marker will not be detected within the zone. Detection of the marker in the Anderson et al. system is not assured unless the entire zone is traversed. For example, a marker having its long axis perpendicular to the floor will only be detected in the center of the zone, but not at the entry and exit points thereof; and a marker having its long axis parallel to the floor and parallel to the plane of the interrogating and receiving coils will be detected solely at entry and exit points and not in the center thereof.
Detection of an article tagged with a Anderson et al. type marker is not assured detection unless the article is moved through the entire zone. This is a matter of severe impracticality in applications where the article to be detected is a surgical instrument or sponge imbedded in a patient under surgery.
Thus, up to the present time, problems presented by post operative retention of surgical implements, though addressed by numerous workers in the art, have remained unsolved. Instead, the detection systems heretofore proposed have failed to account for marker orientation or they have utilized interrogating frequencies that are too high to prevent signal loss through their absorption in living tissue.